OFFSET
0,3
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..1000
T. C. Wu, Counting the Profiles in Domino Tiling, The Fibonacci Quarterly, Volume 21, Number 4, November 1983, pp. 302-304.
FORMULA
If n is even, a(n) = binomial(n, n/2)*n/2.
If n is odd, a(n) = binomial(n + 1, (n + 1)/2)*n/2.
MAPLE
a:= proc(n) option remember;
`if`(n<3, n, (n*(5-7*n)*a(n-1) +4*(n-2)*(7*n+16)*a(n-3)
+(24-12*n+172*n^2)*a(n-2))/ ((n+1)*(43*n-89)))
end:
seq(a(n), n=0..40); # Alois P. Heinz, Oct 20 2012
MATHEMATICA
a[n_] := n/2*Binomial[n + Mod[n, 2], (n + Mod[n, 2])/2]; Table[a[n], {n, 0, 33}] (* Jean-François Alcover, Feb 22 2013, after Joerg Arndt *)
PROG
(Maxima) a[0]:0$a[1]:1$a[2]:2$
a[n]:=(n*(5-7*n)*a[n-1] +4*(n-2)*(7*n+16)*a[n-3]+(24-12*n+172*n^2)*a[n-2])/ ((n+1)*(43*n-89))$
makelist(a[n] , n, 0, 40); /* Martin Ettl, Oct 21 2012 */
(PARI) a(n) = n/2 * binomial(n+(n%2), (n+n%2)/2); /* Joerg Arndt, Oct 21 2012 */
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Marcus, Oct 20 2012
STATUS
approved